1. Field of the Invention
The present invention relates to a wireless communication method and a wireless communication system that perform a multicast transfer in a wireless communication network that communicates through the time division multiple access (TDMA) scheme.
2. Description of the Related Art
Lately, many of wired networks have been replaced by wireless networks, indicating a more and more increasing need expected for wireless communication techniques in the future. The rapidly improved wireless communication speed has enabled wireless communication of data involving a large volume and a real-time requirement, such as moving image and voice data. Increasingly common situations are therefore building home-based wireless networks that connect electronic devices at home over wireless networks and communicating wirelessly with a plurality of notebook personal computers (PCs) and projectors at corporate conference rooms.
In wireless communication networks including a plurality of wireless communication devices, a receiving station, on normally receiving a data frame, typically transmits an acknowledgment (ACK) frame to a transmitting station. Having received the ACK frame, the transmitting station determines that the data frame has been normally transmitted, thus completing transmission of the data frame. If not receiving the ACK frame within a predetermined period of time, the transmitting station determines that the data frame has not been transmitted normally and retransmits the data frame to receive the ACK frame, or repeats retransmission until a prescribed number of retransmissions is reached. This technique is called an automatic repeat request (ARQ) and improves reliability of wireless communication. Another technique is to repeat the retransmission until a lifetime period of the data frame expires.
In commonly established wireless communication standards, however, the ARQ technique is used only in unicast communication that involves only one transmitting station and one receiving station. The ARQ technique is not applied to multicast communication involving a plurality of receiving stations. The multicast communication is expected to be employed in a case in which a handout is to be transmitted simultaneously to a plurality of notebook PCs in a conference room or a case in which a presentation file is to be transmitted simultaneously from a notebook PC to a plurality of projectors, for example. The transmitting station is, however, unable to determine whether all of the receiving stations have received data normally.
Various techniques have been developed to solve the foregoing problem. Specifically, Japanese Patent No. 4152880, for example, discloses a method in which, in order to enhance reliability in multicast transfer, a multicast frame is transmitted after a bandwidth is acquired through transmission of a request-to-send (RTS) frame, a list of IDs of devices that transmit an ACK frame is set in the multicast frame, and wireless communication devices set in the list transmit the ACK frame.
Japanese Patent Application Laid-open No. 2008-17306 discloses another wireless communication method in which, in order to enhance reliability in multicast transfer, an ACK frame transmission time for a multicast frame is previously established and, when the specified time arrives, a wireless communication device that has received the multicast frame transmits ACK frames for all multicast frames received at once.